< Changes
Improve the Anaconda Btrfs preset
Summary
A few small changes will make it easier to do snapshots and rollbacks on btrfs, in the near future.
Owner
- Name: Chris Murphy
- Email: chrismurphy@fedoraproject.org
- Product: Anaconda
- Responsible WG: Workstation, KDE SIG
Current status
- Targeted release: Fedora 33
- Last updated: 2020-06-15
- FESCo issue: <will be assigned by the Wrangler>
- Tracker bug: <will be assigned by the Wrangler>
- Release notes tracker: <will be assigned by the Wrangler>
Detailed Description
/boot will be on btrfs. This is supported by GRUB for ~10 years, and recently in the installer. It will make snapshotting of /boot possible, to ensure parity with /usr on rollback.
Use subvolumes for the following mountpoints: /home /var/logs /var/lib/libvirt/images. This will make it possible to avoid snapshot and rollback of logs, VM images, and user home. NOTE: the design is WIP, but also is not user facing.
Prior work in this area: Revisiting How We Put Together Linux System containers/bubblewrap
Feedback
One big file system? What about clean installs and using /home?
Anaconda custom partitioning will let you reuse an existing 'home' subvolume to mount at '/home', without a reformat. A new 'root' subvolume must be created for '/' however. NOTE: Subvolumes are a bit special, but act mostly like directories, including having no size.
Benefit to Fedora
Optimize the 'btrfs preset' installation for today's use cases, and prepare for additional features. A significant benefit of btrfs is it can be a nearly drop-in replacement, and not burden users with learning esoteric things.
Default features:
- One big file system, no longer run out of space on / or /home.
- Full data integrity checking.ƒ
- (Rootless) Podman will use snapshots.ƒ
Available optionally now, integration in the near future:
- cgroupsv2 IO isolation, completes the resource control picture for better system responsiveness.ƒ
- Transparent compression, file system/directory/file level granularity.ƒ
- Snapshots and rollbacks, restore files using reflink copy.ƒ
ƒ These are btrfs only features.
Scope
- Proposal owners:
- Implement /boot on dedicated ~1G btrfs volume with 'boot' subvolume
- Design a subvolume layout focusing on snapshot and rollback functionality, and modify the btrfs preset kickstart accordingly.
- Other developers:
- Bootloader team to review and ack changes related to /boot.
- Anaconda to review and merge changes.
- Might affect dnf snapper plugin behavior.
- Policies and guidelines: N/A
- Trademark approval: N/A
Upgrade/compatibility impact
This change will not apply to upgrades.
How To Test
Install and use the system however you usually do, and it should behave the same.
User Experience
- Transparent in normal use.
- Always-on integrity verifies metadata and data. Corrupt data results in EIO, it never reaches user space. User is notified by kernel message about affected files by path.
- Podman can use snapshots (default) or reflinks+overlayfs, at user discretion. Both are faster and more space efficient operations, than copy up on ext4.
- Users can opt-in to other btrfs features: snapshots, compression, cp --reflink efficient copies, online scrub, btrfs send/receive, at their own pace.
Dependencies
None
Contingency Plan
- Contingency deadline: Revert all changes.
- Blocks release? Yes.
- Blocks product? Workstation/KDE are release blocking desktops.
Documentation
The user is not expected to know btrfs specific things for day to day use.
man 5 btrfs - for information about general btrfs information, mount options, and features.
man btrfs - for information about the btrfs command and sub commands. NOTE: Subcommands can be arbitrarily shortened, as long as it isn't ambiguous. 'btrfs fi us' is the same as 'btrfs filesystem usage'.
- Users and developers alike, may be interested in: